A brush of the type described in the introduction is already known through the U.S. Pat. No. 4,302,863 A.
Said document discloses a brush intended for use in sweeping machines, especially for airfields or streets. This brush has a plurality of cassette elements (brush bridges) intended to be mounted on a cassette element holding member (brush roller) which cassette elements each has a plurality of bristle bunches arranged there along. A body of a said cassette element has recesses (openings) each configured to receive a U-shaped end of a bristle bunch being bent double therein in such a way that the end of the double bent bristle bunch opposite to the U-shaped end projects out of the respective recess, and a securing wire (locking wire) is drawn through the doubled ends of the bristle bunches to lock the bunches against withdrawal at the cassette element.
The bristle bunches of a brush of this type are after approximately 50-100 hours use torn down to such a degree that either the whole brush or the bristle bunches thereof have to be replaced. As the cassette element holding member of the brush is an expensive component and it is time consuming to replace individual bristle bunches the holding member and the cassette elements having the bristle bunches are made separately and then mounted together before use of the brush. One or all of the cassette elements of the brush may therefore fast and easy be replaced when the bristle bunches thereof are so torn down that the result of the sweeping deteriorates.
The major steps of a known method of producing a cassette element intended to be used with a brush of the type defined in the introduction is illustrated through appended FIGS. 1-4.
A cassette element 5b having a plurality of bristle bunches 9b is produced by:                pressing a middle portion 11b of each said bristle bunch 9b down in an associated recess 7b, located at a first outer surface 8b of a body 6b of the cassette element 5b, by means of either a member 21b or by hand, in such a way that the middle portion of a bristle bunch forms substantially a U-shape therein and a first 12b and a second end portion 13b of said bristle bunch 9b extend out of the recess in a direction away from said first outer surface of the body (see FIGS. 1-3), and        securing said middle portion 11b of each said bristle bunch in the respective recess 7b by pressing a securing wire 14b into an opening 22b at a short side 23b of the body 6b and over the bristles 10b contained in a bottom portion 15b of the U-shape of each of the bristle bunches 9b, in a direction perpendicular to the extension of the bristle bunches in their bottom portions, so that the securing wire 14b secures the bristle bunches 9b in the associated recesses 7b by urging parts of said U-shape of each bristle bunch 9b against surfaces of wall 17b and bottom portions 18b of the respective recess 7b (see FIG. 4).        
There are at least two problems related to this method of producing such cassette elements 5b. Firstly, there is a risk that the middle portion of individual bristles 10c (see FIG. 4) are not being pushed down to a proper position, below said opening 22b, in a recess 7b. This results in that the securing wire 14b will be pressed into the cassette element body 6b over the bottom portion 15b of the bristle bunch 9b but under the middle portions of the bristles 10c being out of position with the consequence that these are not secured by the securing wire. This means that a bristle bunch 9b of the brush will be one or more bristles 10c short leading to impaired efficiency of the brush and in the worst scenario these loose bristles 10c will come off during sweeping of a runway and consequently endanger the use of the runway.
Secondly, there is a risk that the middle portion of individual bristles 10b are not being pushed down to a proper position, below said opening 22b, but is positioned at the same height as the opening 22b in a recess 7b. This results in that the securing wire 14b will be pressed into the cassette element body 6b over the bottom portion 15b of the bristle bunch 9b and into parts of the bristles being out of position with the consequence that these might be damaged before pushed down and secured by the securing wire 14b. This means that the damaged bristles eventually will break and come off during sweeping which for instance shortens the life-span of the cassette elements 5b. Also, if a few bristles 10b-c come off from a bristle bunch 9b there is more room for the remaining bristles 10b to move and the damage of the brush might be even worse.
A possible but not desirable solution for solving these problems is to let an operator examine and manually push individual bristles 10c that are out of position down into the associated bristle bunch 9b before the securing wire 14b is arranged. This solution would be related to high production costs and consequently an expensive brush for the consumers.
There is a strong desire of providing a brush of this type with cassette elements having bristle bunches secured to that degree that the bristle bunches or individual bristles thereof may never move out of the position in which they are secured to the cassette element body by the securing wire, i.e. to overcome the common problem with brushes of this type already known. This problem occur due to the poorly developed method for producing a cassette element already known, in combination with lack of an effective way of securing the securing wire over the bristle bunches of a cassette element already known, since a poorly secured securing wire may lead to that individual bristles or even a complete bristle bunch is ripped out of a cassette element during use of the brush, and a bristle bunch with missing or damaged bristles may lead to impaired securement of the securing wire.